title: Local wall thickness in finite element models improves prediction of abdominal aortic aneurysm growth.
abstract: OBJECTIVE
  Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) predicts clinical outcomes better than diameter alone. Prior models assume uniform wall thickness (UWT). We hypothesize that the inclusion of locally variable wall thickness (VWT) into FEA of AAAs will improve its ability to predict clinical outcomes.
  
  
  METHODS
  Patients with AAAs (n = 26) undergoing radiologic surveillance were identified. Custom MATLAB algorithms generated UWT and VWT aortic geometries from computed tomography angiography images, which were subsequently loaded with systolic blood pressure using FEA. PWS and aneurysm expansion (as a proxy for rupture risk and the need for repair) were examined.
  
  
  RESULTS
  The average radiologic follow-up time was 22.0 ± 13.6 months and the average aneurysm expansion rate was 2.8 ± 1.7 mm/y. PWS in VWT models significantly differed from PWS in UWT models (238 ± 68 vs 212 ± 73 kPa; P = .025). In our sample, initial aortic diameter was not found to be correlated with aneurysm expansion (r = 0.26; P = .19). A stronger correlation was found between aneurysm expansion and PWS derived from VWT models compared with PWS from UWT models (r = 0.86 vs r = 0.58; P = .032 by Fisher r to Z transformation).
  
  
  CONCLUSIONS
  The inclusion of locally VWT significantly improved the correlation between PWS and aneurysm expansion. Aortic wall thickness should be incorporated into future FEA models to accurately predict clinical outcomes.
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Eric K
authors.initials: EK
authors.lastname: Shang
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Derek P
authors.initials: DP
authors.lastname: Nathan
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Vascular Surgery and Endovascular Therapy, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Edward Y
authors.initials: EY
authors.lastname: Woo
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Vascular Surgery and Endovascular Therapy, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Fairman
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Vascular Surgery and Endovascular Therapy, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Grace J
authors.initials: GJ
authors.lastname: Wang
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Cardiac Surgery, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Gorman
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Cardiac Surgery, University of Pennsylvania, Philadelphia, Pa.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Gorman
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pa; Division of Vascular Surgery and Endovascular Therapy, University of Pennsylvania, Philadelphia, Pa. Electronic address: benjamin.jackson@uphs.upenn.edu.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Jackson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001012:Aorta, Abdominal / Q000000981:diagnostic imaging* / Q000503:physiopathology; D017544:Aortic Aneurysm, Abdominal / Q000000981:diagnostic imaging* / Q000503:physiopathology; D001027:Aortography / Q000379:methods*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D018450:Disease Progression; D005260:Female; D020342:Finite Element Analysis; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D011379:Prognosis; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D013314:Stress, Mechanical; D013997:Time Factors; D014057:Tomography, X-Ray Computed